add nix flake for development (#1233)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Chores**
- Refined repository settings to auto-exclude environment and
build-related files.
- Introduced a new configuration that streamlines local development and
displays key tool versions on setup.
- **Documentation**
- Expanded contribution guidelines with a dedicated developer resources
section linking to guides on development practices and repository
structure.
- Updated workflow instructions to better assist developers in setting
up their environment, especially for those using Nix.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

api/docs/developer/workflows.md

@@ -215,3 +215,5 @@ unraid-api --help
 5. Test your changes: `pnpm test`
 6. Deploy to a development server: `pnpm unraid:deploy <SERVER_IP>`
 7. Verify your changes on the Unraid server
+
+If using nix, run `nix develop` from the root of the repo before Step 2.